Hypersensitizing photographic film developer



Patented Nov. 24, 1953 HYPERSENSITIZING PHOTOGRAE'HIC FILM DEVELOPERBobbie J. Schultz, Hollywood, Calif.

No Drawing. Application March 25, 1952, Serial No. 278,493

3 Claims.

This invention relates to the art of developing, in photographicnegatives (black and White), the latent image produced therein byexposure to actinic light.

Virtually all photographic negative film used today in the production ofblack and white photographs utilizes, as a light sensitive coating, anemulsion of a silver halide in a gelatin film. The most commonly usedhalides are the silver bromides and the silver chlorides, and thepresent invention deals particularly with the development of latentimages in coatings containing crystals or grains of halides as the lightsensitive ingredient thereof. With conventional developing practices,good negatives can be obtained only from film that has been sufficientlyexposed Within the range of exposures specified for the film.Underexposed film results in a negative having either no image or only afaint image, from which it is impossible to obtain a satisfactory print.

The present invention deals with the problem of recovering asatisfactory negative from an underexposed film, and its general objectis to provide a hypersensitizing developer for intensive developing ofan underexposed film so as to obtain an adequately developed final imagefrom the underexposed latent image on the film.

The fact that latent images in underexposed film can be developed intosatisfactory negatives by a two-stage process starting with a normaldeveloping operation (resulting in a final image that is whollyunsatisfactory, i. e. entirely too undeveloped) followed by a secondarydeveloping operation known as intensification, is generally known.Intensification involves depositing additional silver on a previouslydeveloped weak negative image resulting from an ordinary developingprocess using a standard developer. Intensification processes have notproven to be fully satisfactory. All of them are objectionable becausethey involve two stages of development instead of only one, and aretherefore more time consuming and expensive. One such process, whichutilizes a second exposure of the latent image to a light of lowintensity, has the further objectionable result of grading down orfogging the entire image. Another such process, in which the latentimage is exposed to ammonia fumes, also causes some fogging. Still athird, utilizin exposure to mercury vapor, is impractical due to thelength of exposure time required.

The present invention is directed toward a hypersensitizing process (asingle operation development rather than to a multiple stageintensification process). Many attempts have been made, of course,throughout the history of photography, to increase the sensitivity ofdeveloping processes so as to extend the range of utilization ofunderexposed latent images in the production of satisfactory finalimages in a single development operation. One of the problems that hasbeen faced in all such endeavors, is that of obtaining simultaneously,in a single development operation, satisfactory final images from bothunderexposed and adequately exposed latent images.

A convenient measure of amplification of image development obtained fromintensification and hypersensitizing processes, over the resultsobtained from conventional development practices, is in terms ofincrease in the speed" of the film as indicated by the results of suchextraordinary processes, over the normal specified speed of the film asdetermined by the results of standard development practice. Based onthis measure of improvement the greatest increase in film speedpreviously obtainable through hypersensitizing has been in theneighborhood of five times normal film speed. That is to say,hypersensitizing has, up to the present time, been capable of utilizinga latent image produced at approximately one fifth the exposure periodrequired for a good final image under standard development practices.The best results obtained in the use of intensification processes havebeen an increase to ten times normal film speed.

It is widely understood that the commonly available emulsions of todaymust have a certain minimum exposure in order to obtain any picture atall. According to all photographic development exposure theories, thestandard ratings of film speed or emulsion sensitivity are based on theproposition that the exposure cannot fall below the minimum determinedby the Weston rating of the film, if satisfactory pictures are to beproduced. Any substantial deviations in exposure, outside the rangeindicated by the Weston rating, is commonly understood to result in noimage at all; or, if presently known hypersensitizing or intensifying oroverdeveloping methods are practiced, only the high lights (areas ofmaximum exposure) will build up to a printable density. To my knowledgethere has never been previously made available any developer or methodwhereby more than ten times the normal exposure rating the normalexposure time) can be utilized in exposing film, and even with the useof the known hypersensitizing or intensifying methods, the high lightsusually build up so 3 much faster than the shadow areas that the resultsare entirely unsatisfactory Or unusable in the minimum exposure portionof such range of reduced exposures.

The common understanding that it is impossible to drop much below thecommonly understood minimum exposure for any given film, is sowidespread as to be known generally as the threshold of exposure belowwhich there is insufficient light striking the negative to produce anyimage. The threshold is commonly plotted on a graph as a toe of a curvedline indicatin film speeds, processing time, etc. It is my belief thatthis toe may be simply the top one in a series of such toes risingsteplike from a point far below anything that has previously beenconsidered at all within the range of possibility. If this belief iscorrect, current film speed ratings may represent, not the minimum, butrather, the maximum of exposure that can be given to a negative.

The invention involves the discovery of a hypersensitizer which givesexcellent results far beyond the range previously attained as indicatedabove. To illustrate the results, I have, using my developer, obtainednegatives of good quality from exposures up to one hundred times thespecified Weston ratings for such film (i. e., down to one percent ofthe degree of exposure specified for such film). These results have beenobtained in research utilizing principally the Eastman Kodak CompanysPlus -X roll film (which has a Weston rating of 50 for standard exposureand development practices), in unbelievably short exposure periods ofbetween 4000 and 6000 Weston. In this connection it will be understoodthat an exposure taken at the Weston rating of, e. g., 5000 Weston, willadmit only one percent of the light which is admitted in an exposure of50 Weston rating. Accordingly, it is apparent that the present inventionproduces an increase in ratio from the :1 ratio, the highest ratiopreviously attained, to a 100:1 ratio, ten times as great.

Furthermore, I have succeeded in obtaining these results withoutsacrificing resolution of the image, i. e., without substantialdistortion of the relation between highlights and shadows.

With the foregoing in mind, the general object of my invention is toprovide a hypersensitizing developer and a hypersensitizing concentratefor producing such developer, which produces a much higher degree ofhypersensitizing than has hitherto been possible, such as to obtain goodnegative images from slight exposures produced as low as one hundredtimes below standard specified exposure levels.

The problem of the photographer has long been that of sacrificing onething for another (e. g., shutter speed for depth of field, etc.). Thepresent invention opens up an entirely new field of possibilities forthe photographer, in making it possible to utilize as low as one percentof the light formerly considered necessary for a proper exposure. Bythus making it possible to reduce exposure time to undreamed ofshortness, the invention provides a wide latitude of selection of smallcamera apertures for sharpness of detail, depth of field, etc. In fact,it makes it possible to approach the ideal aperture, i. e. the pin-pointtype of camera aperture which is in focus for practically every depthfrom the most distant up to within but a few inches of the cameraobjective.

With the great increase in film speed which my developer makes possible,a photographer can now take pictures under lighting conditions which at4 present virtually make it impossible to obtain any picture at all. Forexample, good pictures may be obtained on heavily clouded days, undertwilight conditions, and even by moonlight, using conventional film nowuseable only for daylight pictures or pictures taken with the aid ofstrong fioodlights, or flashlights.

It is of course necessary to properly relate the development of thenegative to the exposure conditions. This can be done either byshortening the development time, for exposures of greater intensity thanthe minimum which is made possible by the invention; or by adjusting theexposure for adopting a substantially standard development practice suchas to utilize maximum film speed without departing from optimum resultsin the resolution of the image, and adjusting to fit such optimumdevelopment practice. Thus the taking of pictures on a heavily cloudedday, with apertures inside the range ordinarily used for full sunlightexposures, would be common practice, and for full sun exposures, theaperture would be stopped down far below the common range of apertures,or the shutter speed would be increased to a point far above the normalrange of shutter speeds, or some combination of aperture reduction andincreased shutter speed would be utilized. The taking of action picturesnecessitating extremely fast shutter speeds would likewise becomepossible with the standard snapshot film now provided, and it would notbe necessary to utilize the high speed films commonly used for suchaction pictures.

All of the foregoing improved results are included among the objects ofmy invention.

My improved hypersensitizer concentrate is characterized generally bythe use of formic acid as an active ingredient thereof. Moreparticularly, the invention is characterized by the combination offormic acid with ammonia, glycerine, and 6-nitrobenzirnidizole (asubstance commonly used as an anti-fog agent) to produce theconcentrate.

The following examples illustrates typical hypersensitizer concentratesembodying the invention:

Example I Spirits of ammonia-10% NHiOH64 drams Formic acid-HC0.0H32drams fi-nitrobenzimidizole (dry)-12 grains Glycerine-4 drams Thefunctions of the several ingredients are as follows:

Ammoniaactive hypersensitizing agent Formic acidactive hypersensitizingagent 6 Nitrobenzimidizole-fog inhibitor Glycerinebinder for ammonia TheG-nitrobenzimidizole which I have employed, is, specifically, EastmanKodak Company Anti-Fog #2, in powdered form, sometimes referred to as A.F. #2.

Preparation.The hypersensitizer concentrate is prepared as follows:first, the prescribed amount of 6-nitrobenzimidizole powder is dissolvedin four ounces of formic acid. This is S It is to be understood that theproportions of the ingredients may be varied to some extent within thescope of the invention. The range of possible variation i indicated bythe following additional examples of the concentrate.

Example I] solution NH4OI-I64 drams BOOGIE-32 drams G-nitrobenzimidizole(dry)--12 grains Glycerine-4 drams Formaldehyde (HC'OH)-1 to 8 dramsThis formula will provide for additional hardening and help to preventswelling of the emulsion, for use in extremely high temperatureprocessing. The degree of hardening may be controlled by the amount ofHCOH added to the standard formula.

The addition of the HCOH to the formula necessitates an increase in theamount of hypersensitizer solution added to the standard developer. Suchincrease in the amount of concentrate to be added to the standarddeveloper may ordinarily be determined as roughly twice the amount ofHCOH that is added to the concentrate, i. e., for each 2 drams of HCOHthat is added to the concentrate, 4 additional drams of the concentratewill be added to the developer.

Example III 10% solution NH4OH21 drams HC0.0 I-I32 drams 6nitrobenzimidizole (dry)--l2 grains Glycerine4 drams This formula doesnot produce quite as intense an action as the formulas of Examples I andII.

Example IV NH4OH'128 drams HC0.0H32 drams fi-nitrobenzimidizole (dry)-12grains Glycerine-4-8 drams DEVELOPER The concentrate is utilized byadding a small quantity thereof to a standard developer. For example, inthe use of the concentrate disclosed in Example I above, from 27 to 60drops of the concentrate are added to 16 oz. of standard developer.

In developing negatives in the developer thus produced standarddeveloping practice is followed except that the developing time is fromone and a half to two times the normal developing time. An 80 F.temperature is observed in the developer solution.

The following examples illustrate the developer of my invention:

Example I WaterI-I2Oat 125 F.l quarts Elon (methylaminophenol sulfate)-HO'CGH (NI-ICHs) /,;H2S04360 grains Sodium sulfite-NazSQsJ7H2O4 ouncesHYdI'OQHIDODMGH (OI-I) 2-400 grains Sodium oarbonateNa2OOs2 ouncesPotassium bromideKBr-200 grains Ammonia solution10% NH4OH2 drams .5%6-nitrobenzimidizole2 drams Formic acidHC0.0H--2 drams Hypersensitizerconcentrate (Example I above)- 6 drams Water up to 2 quartsPreparation-In the preparation of the developer, the chemicals namedabove are dis solved in the order named, starting with the 1 quarts ofhot water, then adding the elon, sodium sulfite, hydroquinone eto.,successively. As the final step, the indicated quantity of cold water isadded to the solution to dilute it to the proper strength. A precipitateof calcium, elon and sulfite may be formed during the mixing process. Ifthis occurs, the precipitate should be carefully filtered out of thesolution. After the solution has cooled to room temperature, thedeveloper is ready for use.

Where an emphasized tanning efiect is desired, the sodium carbonate maybe replaced by sodium sulfate, without sacrificing the function of thecarbonate. Thus the developer may comprise:

Epulmple II It is to be understood that the quantities of chemicals inthe hyper-developer may be varied and the results remain fairly constantover some range of deviation; provided a near proportion is maintained.

The following example will illustrate:

Example III Elon (methylaminophenol sulfate)- HOCsH4 I-I2SO4-180 grainsSodium Su1fiteNa2SO3.7I-I2O2 ounces Hydroquinone-CsH4(OH)2-400 grainsSodium carbonate-NazCOs1 ounce Potassium bromide-KBr-l00 grains Ammoniasolution-l0% NHlOH-2 drams .5 %-6-nitrobenzimidizole2 drams Formicacid-HCO.OI-I1 drams Water to make2 quarts Aerosolounce H2O'1 quartsExample IV Elon (methylaminophenol sulfate)- HOCsHe 1/2H2S04-29O grainsSodium sulfite--Na2SO3.7HzO8 ounces Hydroquinone-C6II4(OH) 2--1 /2ounces Sodium carbonateNa2COel ounces Potassium bromide-KBr--400 grainsAmmonia solution-40% NH4OH1O drams .5%-6-nitrobenzimidizole-1O dramsFormic aoid-HC0.0H9 drams Water to make2 quarts Aerosol--2 ouncesI-IzO-N/ quarts Example V Water-I-hO-at F.1 quarts Elon(methylaminophenol su1fate) HOCsI-Ie (NI-ICI-Ia) /2H2SO'4-360 grainsHydroquinone-CsH4(OI-I) 2400 grains Sodium carbonate-Na2CO32 ouncesPotassium bromide-KBr200 grains (Example I Ammonia solution-10% NH4OH-6drains Formic acidHC0.0I-I4 drams .5%-6-nitrobenzimidizole3 drams Waterto make-2 quarts Aerosol-1 ounce The addition of Aerosol merelyincreases the life of the developer and allows it to go into action onthe negative faster and more evenly. Aerosol is a trade-name for one ofmany wetting agents which break the surface tension and allow the liquidto saturate more evenly, quickly and completely.

USE OF DEVELOPER For best results, the user will indulge in someexperimentation with the solution. However, as .a starting point, goodresults may be obtained by developing for approximately twenty minutes,at 80 F. negatives which have been exposed at 4000 Weston ratings. Acorrespondingly longer developing period will be utilized for lower filmspeeds.

It may be noted from the foregoing Example I of the developer, thatseveral of the ingredients of the concentrate (for example the ammoniaand nitrobenzimidizole ingredients) are repeated in the concentrate andin the developer to which the concentrate is added. Formic acid is addedto the developer separately and also as an ingredient of theconcentrate. One of the functions of the concentrate is to increase theproportions of the common elements.

In the foregoing developer the hydroquinene functions in its normalcapacity as a reducing or developing agent, reducing the silver halideIn any developing process, it is probably true that, when the developingprocess is arrested, the various grains of the emulsion will be arrestedin various stages of conversion from silver halide to metallic silver,depending upon the amount of light which has been received by therespective grains. That is to say, the more highly exposed grains willundoubtedly be converted into silver more rapidly, during thedevelopment process, than the less highly exposed grains. In thehypersensitizing and hyper-developing process which results from the useof my improved hyper-developer, it is believed that the same generalrelationship between the progres sive stages of development of the morehighly exposed grains and the less highly exposed grains, is maintained,but that the developing process for all of the grains is speeded up sothat the same or equivalent results are secured from greatlyunderexposed emulsion as is secured by ordinary developing methods fromemulsions with standard exposures. Stated somewhat differently, it nowappears that even very, very slight exposures of the emulsion grainswith the various graduations of exposures resulting from the differencesin light coming from the dark and light parts of the subject, can beutilized to start' the process of developing the various grains, andthat, through the use of the hyperdeveloper these very slightly exposedgrains may be brought up through a relatively long stage of developmentfrom the very slightly exposed condition thereof, to the final stage ofdevelopment in which a satisfactory negative is produced, the same as,in standard developing procedures, the much more heavily exposed grains,but with the same relative differences of exposures in the light anddark areas of the picture, will be brought, to substantially the samefinal stage of development, through a range of development which may beconsidered as only a small fractional, terminal portion of the entirerange of development utilizing my improved developer.

This theory appears to be consistent with the fairly widely acceptedtheory concerning the nature of the conventional film developingprocess. According to that theory, the silver halide grain is a crystalconsisting of a regular assemblage of positively charged silver ions andnegatively charged halide ions. It is assumed that each crystal ofsilver halide contains interstitial silver ions, that is, ions displacedfrom their normal position in the crystal. Light rays impinging upon thecrystal liberate electrons from the bromide ions. These electrons attachthemselves to the sensitivity centers, which are believed to be nucleiof silver sulphide scattered throughout each silver halide crystal. Asthe electrons attach themselves to the sulphide sensitivity centers,they acquire a negative charge. Consequently they attract the positivelycharged interstitial silver ions, which move up to the centers, wherethey combine with the electrons to form neutral atoms of silver. Theseatoms, in conjunction with the sensitivity centers, constitute thelatent image.

If this theory is correct, it will be apparent that the action of thedeveloper is to carry forward the incipient conversion of silver halideto neutral metallic silver atoms, which has been initiated by theexposure of the silver halide crystals to light. It will also beapparent, if we assume that the degree to which the conversion has beenadvanced by the light exposure is proportional to the amount of lightfalling on respective grains, that the various sensitivity centers Will,in the latent image, be in various degrees of advancement of theconversion process. It also seems logical to assume that, as theconversion is carried forward in the developing process and enters thevisual image stage wherein the density of the collodial metallic silverwhich has been collected around the sensitivity centers, becomessuii'icient to bring out the characteristic black color of the collodialsilver, that each sensitivity center will maintain a relative positionof advancement of the process, corresponding to its relative position ofadvancement in the latent image.

Based upon the foregoing assumptions, it may be considered that, in thedevelopment of a visible negative from a latent image on a very slightlyexposed film, using my improved developer, that the developing rocesssimply commences at a much earlier stage in the evolution of metallicsilver from silver halide at the sensitivity centers, and that, at thevery terminal stage of such development, the process parallels theconventional development process beginning with a latent image resultingfrom a heavy exposure.

I claim: 7

1. A photographic negative developer containing methylaminophenolsulfate, sodium sulfite, hydroquinone, sodium carbonate, potassiumbromide, ammonia, 6-nitrobenzimidizole, and water and, in addition,formic acid functioning as an hypersensitizing agent for developing fullimages irom latent images which, according to exposure rating of thefilm, are highly underexposed.

2. A photographic negative developer containing methylaminophenolsulfate, sodium sulfite, hydroquinone, sodium carbonate, potassiumbromide, and water and containing in addition, as an hypersensitizingagent for developing full images from latent images which, according toexposure rating of the film, are highly underexposed, a combination offormic acid, ammonia, 6-nitrobenzimidizole and glycerin in the followingproportions:

Spirits of ammonia-40% NH4OH-64 drams; Formic acid-I-IC0.0H--32 drains;B-nitrobenzimidizole (dry)12 grains; Glycerine--4 grams.

3. A developer for intensified development of photographic negatives,comprising a combination of a standard developer having the followingingredients in the proportions stated:

and, as an hypersensitizing agent for developing full images from latentimages which, according to exposure rating of the film, are highlyunderexposed, a small portion of a hypersensitizer concentrate additiveconsisting of the following ingredients in the following proportion:

Spirits of ammonia-10% NH4OH-6 l drams; Formic acid--HC0.0H32 drams;6-nitrobenzimidizole (dry)-12 grains; G1ycerine 4 grams.

BOBBIE J. SCHULTZ.

No references cited.

1. A PHOTOGRAPHIC NEGATIVE DEVELOPER CONTAINING METHYLAMINOPHENOLSULFATE, SODIUM SULFITE, HYDROQUINONE, SODIUM CARBONATE, POTASSIUMBROMIDE, AMMONIA, 6-NITROBENZIMIDIZOLE, AND WATER AND, IN ADDITION,FORMIC ACID FUNCTIONING AS AN HYPERSENSITIZING AGENT FOR DEVELOPING FULLIMAGES FROM LATENT IMAGES WHICH, ACCORDING TO EXPOSURE RATING OF THEFILM, ARE HIGHLY UNDEREXPOSED.